Valves are mechanical components that aid in regulating the flow of material capable of flowing through a pipe, such as a gas or liquid, in order to provide specific pressure or flow rate values. Valves are normally made up of three basic elements, namely:                (1) a body that contains a movable member (a shutter) that connects to the pipes within which the fluid flows;        (2) the shutter that allows the interception of the fluid;        (3) control units, which can be manual, electric or magnetic, that move the shutter.        
Valves can be classified by design shape (for example, ball, butterfly, gate valves), by type of operation (for example, manually operated, driven by actuators with electric, pneumatic and hydraulic control) and/or by application (for example, as regulating and shut-off valves).
The control of subsea valves is an important concern of the petroleum industry due to the large expense and risks associated with oil spills. For example, BP (formerly British Petroleum) has had to set aside over forty-three billion dollars to cover fines, legal settlements, and clean-up costs related to a 2010 oil spill in the Gulf of Mexico.
As the exploration for oil and gas moves into deeper waters, the problems and expense associated with such activities will only increase.
Known systems employed for controlling the opening and closing of undersea valves include hydraulic, pneumatic or electro-hydraulic actuators. These actuators typically utilize an externally controlled flow of pressurized hydraulic fluid to drive a piston within the actuator cylinder. This cylinder compresses a spring stack and moves a valve stem to open or close the valve. In a subsea environment, actuators should be manufactured with a fail-resistive closing configuration to prevent or at least severely limit leakage. In an emergency situation, when the valve must be closed quickly, the potential energy stored in a compressed spring is often employed.
Ideally, actuator configurations should entirely prevent the leakage of fluid being controlled. As used herein, the term “fluid-resistive actuators” is meant to encompass not only actuators that prevent leakage, but also actuators that in practice severely limit leakage except to a very small extent.
Traditionally, hydraulic spring return actuators have been employed to move valves in subsea actuators. Hydraulic actuators typically utilize fluid transported through a line extending to the surface, or from an accumulator located on the seabed at or near the well.
Hydraulic actuators suffer a number of disadvantages for subsea applications. As the distance between the actuator and the topside control center increases, the amount of hydraulic fluid needed to fill the lines and operate the valves increases. Over long distances the fluid can lose pressure. Therefore accumulators have to be installed near the actuator to back up the pressure. In addition, the time between a signal being sent from a control center and the actuator responding can be a matter of minutes. In emergency situations this can be too long.
Increases in water depth can also affect actuator performance. The cost and size of hydraulic lines and umbilicals increase with the operational depths and distances.
Existing electric actuators solve some of the problems involved affiliated with hydraulic actuators, however they suffer from their own problems. In particular, as they rely on electric power to open and close the valves, even a short-time power loss prevents existing actuators from closing, which is undesirable and can lead to disastrous consequences in the case of subsea operations.